The invention relates to a drive for a flap provided on a vehicle.
Moreover, the invention relates to a pedestrian protection means on a motor vehicle comprising an above mentioned drive.
Today""s automobiles are often provided with drives for the various flaps on the car concerned, including a vehicle door, a trunk lid or gas tank cover and especially an engine hood. Especially with regard to the attachment of engine hoods to the car body, pedestrian protection is to be improved in motor vehicles in that the engine hood is to be made more yielding. For this purpose, thought has been given, for example, to airbags for pedestrians or to a yielding suspension of the engine hood.
The invention provides a very simple and effective drive that can be used, for example, for a pedestrian protection means comprising the engine hood. The drive proposed is configured in such a way that it raises the engine hood by a defined amount if a pedestrian is detected by an accident sensor. The engine hood is suspended in an elastically yielding manner by this amount so that the impact for the pedestrian is not as hard. The drive is capable of raising the engine hood within a few milliseconds. Moreover, it is capable of being used multiple times for the same purpose without having to go to the repair shop, an important aspect in view of the fact that the accident sensors may not always detect beyond all doubt a collision with a pedestrian but rather, for example, also with objects, for example, a box, which do not cause damage in case of a collision with the vehicle. A pyrotechnical drive device would have to be replaced at great expense after each actuation event that turned out to be unnecessary.
The drive proposed is, in particular, intended for use with an engine hood, but can likewise be used as a drive in the form of e.g. a closing means for a vehicle door or for another flap. The drive is distinguished by a simple structure and comprises an electric motor, an actuation shaft that is connected to the flap, and a reduction gear by means of which the rotor of the electric motor is coupled to the actuation shaft. The drive further comprises an energy accumulator by means of which the actuation shaft can be driven independently of the electric motor. The reduction gear is configured in such a way that the actuation shaft is driven in a rotational direction only by the energy accumulator and the electric motor drives the actuation shaft in a rotational direction opposite to the rotational direction called opposite rotational direction, thereby supplying to the energy accumulator an energy that is needed to drive the actuation shaft in the rotational direction.
The energy accumulator moves the flap, especially the engine hood, abruptly out of its original position into the desired raised position and the electric motor moves the flap back into the original or starting position against the resistance of the energy accumulator, in order to xe2x80x9carmxe2x80x9d the energy accumulator once again.
According to one embodiment, the energy accumulator is firmly coupled with the actuation shaft. This means that no complicated coupling mechanisms are provided between the actuation shaft and the energy accumulator and/or the electric motor.
According to the preferred embodiment, the reduction gear is configured in such a way that it can be moved into a release position in which the energy stored in the energy accumulator is abruptly released so as to drive the actuator shaft. This means that the electric motor has multiple functions. On the one hand, it moves the flap back into the starting position and, on the other hand, it itself releases the energy accumulator by moving the reduction gear into the release position. In order for this to be possible within an extremely short period of time, the electric motor and the gear have to be designed with as little inertia and loss as possible. For this purpose, the electric motor is a brushless internal rotor that is not very susceptible to dirt deposits and the moving parts of which have a low inertial mass.
The reduction gear preferably has a toothed wheel that has no teeth on part of its circumference (toothless area). As soon as the toothless area is rotated so as to be vis-à-vis the toothed counterwheel, which is done by the electric motor, the release position is reached and the toothed counterwheel can rotate freely since the energy accumulator is activated. In the release position, the electric motor is then uncoupled from the actuation shaft.
Outside of the release position, the energy accumulator and the rotor of the electric motor are rigidly coupled to each other mechanically by means of the reduction gear.
The invention further relates to a pedestrian protection means provided on a vehicle and equipped with a drive as described above. The pedestrian protection means which is proposed has an engine hood and at least one drive to move the engine hood, the energy accumulator raising the engine hood in case of an accident out of an original position into a raised position and holding it in the raised position in an elastically yielding manner. The electric motor then can move the engine hood back into the original position. This means that the energy accumulator likewise has a double function in that, on the one hand, it raises the engine hood and, on the other hand, it ensures the yielding suspension of the engine hood in the raised position, so that the impact of the pedestrian on the engine hood is not so hard. Preferably, the energy accumulator is a spring energy accumulator, especially a spring energy accumulator with a spiral spring.